Center Main Oil feed

S

SAXBY2

Senior Member
Attached are 2 options found for center main oiling.
A. What is the triangular plate that appears to accept the pipe fitting and where the oil pump
drops on to ?
B.Is the oil line tapped in to the block side face and how does that accept oil from
the galley ? (Glyptal painted block)
 

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On Model A standard, the center mail is normally oiled by "gravity" from a drilled passage from the "floor" of the valve chamber.

On a Model B standard, the center main is normally oiled by "semi-gravity" from a drilled passage from the alongside oil gallery (you can see this with the valve chamber cover "off" with a separate chamber the length of the valve chamber.)

You don't say Model A or Model B on these.

Now you also don't say if these blocks have been modified for "pressure" oiling. The glyptal coated block would be typical where the oil pump receiver neck/cylinder block has been drilled and a separate passage provided directly from the oil pump discharge.

The other block I'm not sure of. There must be an oil pump SOMEWHERE.

Those who convert to pressure blocks may recognize either or both of these modifications better.

Joe K
 
the first picture - a hole has been drilled into the oil pump boss, then tapped for a fitting. that would direct some of the oil to the center main cap.

the second picture - seams to be the same idea except they drilled straight up / vertical and probably a second drill hole horizontal to intersect it. then tapped for the fitting

both are the same result buy accessing the oil coming up through the oil pump boss.

i don't think there is a plate on it that is just the opening the oil pump goes into.

those pictures are Model A engines not B
 
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The one without the oil pump must have a pump driven off the side of the timing gear.It sure can't go where that pipe is adapted into it.Seems I've seen side mounted oil pumps on aircraft applications.
 
Pietenpol Air Camper seems to have been an early candidate for "pressurized oil system" to include an available "kit" to convert the Model A engine to pressure oiling.


Joe K
 
If you zoom way in on the second photo you will see the hole for the oil pump behind the fitting. The "triangular" thing is an L shaped bracket that holds the fitting. The bracket appears to be captured by the oil pump.
 
I see the hole where the peg on the oil pump fits,the one that keeps it from rotating,but that fitting in the big hole is where the oil pump body and shaft goes.That copper line and it's fitting would have to be removed to put the oil pump in it's original position.
 
nkaminar said:
If you zoom way in on the second photo you will see the hole for the oil pump behind the fitting. The "triangular" thing is an L shaped bracket that holds the fitting. The bracket appears to be captured by the oil pump.
Click to expand...

I agree with NK, the oil pump is just not installed. I think it is an optical delusion that the fitting is going in the oil pump hole.
 
is there a reason why they are only supplying only the center main? wouldn't a person plumb all three mains?
 
Center main takes much worse abuse than the other two and wears much faster. If you were able to prevent it from wearing down, you would dramatically extend the amount of time before the engine needed to be overhauled.
 
So which option is thought to be the best for the oil collection port, drilling horizontally into the oil pump shaft or vertically in to the oil gallery / valve chamber ?
 
I can't speak to the application of pressure oiling to the Model A engine specifically, but in "modern" engine design, the quantity and pressure to each bearing is calculated to "float" the journal centrally within its bearing. Hence the use of circumferential oil grooves rather than the "x-x" grooves of an earlier methodology.

Modern engines actually "don't touch" their bearings - rather the journals "float" on hydro pressure of the bearing.

That's a big statement and an objective that can be realized in practice. Obviously startup (before oil pressure is established) shutdown (after the collapse of oil pressure) or heavy load (when the lateral bearing loads exceed the hydraulic pressure) the statement is obviated.

EMD diesels actually have a "wear pattern" resulting from startup/shutdown where one can see the actual "touch" of the journal on bearing. I expect other engines are similar.

Now in the case of a Model A engine, the best situation would be insert bearings and the bearing annular oil gallery connected "directly" to a pressure header from the oil pump. No "gravity oil" from a Model B gallery or the Model A valve chamber floor. Accomplishing this in practice is the challenge. I have seen somewhere that 20-35 psi is a "good oil pressure" - if in reality it can be maintained

And, of course, there is the additional technical challenge of "drilling the crank" to afford pressure oil to the rod bearings. And possibly why the Model B crank is preferred for this level of modification.

Joe K
Too many EMD Gensets in my past.
 
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My understanding is that the Model A bearings also use a hydrodynamic wedge to float the journal inside the bearing. The center main journal is simply too small and the crankshaft flexes too much under load, so it exceeds the capacity of the wedge pretty often, especially since the only thing pushing the oil into the bearing is the scoop on the outside of the crank as it dips into the sump.
 
alexiskai said:
My understanding is that the Model A bearings also use a hydrodynamic wedge to float the journal inside the bearing. The center main journal is simply too small and the crankshaft flexes too much under load, so it exceeds the capacity of the wedge pretty often, especially since the only thing pushing the oil into the bearing is the scoop on the outside of the crank as it dips into the sump.
Click to expand...

As far as I know, the only source of oil for any of the main bearings is from holes drilled down through the block from the valve chamber. If you look inside one, you'll see them. The scoops you refer to supply oil only to the con rod bearing.
When I built me "work horse" engine, I pressure fed the middle main bearing AND installed a harmonic balancer. Both pressure feeding oil to the bearing will extend its life as has been said above and the balancer will do the same. I decided not to make the either/or choice so I used both. I'm not sure which will last longer, the engine or me!
 
The hydrodynamic wedge is what floats the journal in the bearing. It is generated by the turning of the journal. Startup is hardest on any journal bearing.
 
Synchro909 said:
When I built me "work horse" engine, I pressure fed the middle main bearing AND installed a harmonic balancer.
Click to expand...


That’s what I intend to do on my next build. Plus counterbalancing the crank and reducing overall rotating assembly weight, if I can find affordable parts. The center main is the Achilles heel of this engine.
 
alexiskai said:
That’s what I intend to do on my next build. Plus counterbalancing the crank and reducing overall rotating assembly weight, if I can find affordable parts. The center main is the Achilles heel of this engine.
Click to expand...

Indeed it is but it was not confined to Model As. I think all 3 main bearing 4 cylinder engines of the period were like that.
 
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